The invention is based on a plunger system in a brake line between a master brake cylinder and a wheel brake cylinder of a vehicle, for modulating a brake pressure when there is a sensor-detected danger of locking the wheels of a vehicle, one plunger system required for each driver wheel. In German Auslegeschrift No. 22 12 912, an anti-lock or anti-skid system for motor vehicles is shown that has a brake force reducing means inserted into the brake line leading to the rear axle. This brake force reducer has a flow monitored by a valve and controlled by a rod, and it has a reducing plunger that under the influence of fluid pressure closes off this flow. Closing off the flow takes place whenever one wheel of the rear axle is locking or skidding. To this end, a pressure exchange chamber is put under pressure, and the reducing plunger closes the valve.
Although effective skid protection can be attained with this system, nevertheless it has no effect when wheels are spinning, when a drive slip regulating means must be operative.